Small Engines (Lawn Mowers, etc.): Lawn mower pull start won’t pull, briggs stratton engine, briggs stratton

Question
I have a one year old Craftsman mower with a 675 Series Briggs & Stratton Engine (Model No. 944.368610) that has worked fine til now.  Haven’t started it since last September. Just filled up the gas tank with fresh gas.  Started on the third pull (accidentally let go of pull rope and it briefly wrapped around the handle - not sure if that matters).  Everything sounded fine.  When I engaged the self-propelled mechanism with the hand bar, the engine stopped abruptly. WehenI tried to restart the mower, the pull rope would only come out about 6 inches, no further.  I know just about nothing about small engines so any advice should be in the most basic language possible.  Thanks

Update: So I took off the shroud(?) over the self-propelling motor, sprayed some WD40 around. I also tipped the lawn mower and moved the blade by hand, which was somewhat stiff and hard to rotate.  I sprayed a little WD40 up where the blade attaches and it became a bit easier to move.  When I tried to start the mower again, the pull start rope did pull, albeit somewhat stiffly, and the mower did actually start (which is a good thing because my lawn is embarrassingly long).  I cut the lawn without engaging the self-propelling mechanism, and the engine sounded a bit labored but I was able to stop and restart a few times.  Once finished, I attempted to engage the self-propelling mechanism and it moved the front wheels at first (for about 10 seconds) and then the front wheels wouldn’t turn.
Thanks again.

Answer
Can you turn the front wheels by hand?  

Did you try removing the belt to see if the engine is less labored?  

Does the engine run alright other than when you engage the self-propel?

Sounds like there may  be a problem with the drive system.

Eric